The coronary artery diameter is influenced by gender, age, anatomic variation, and certain physiological and pathological processes (Yang et al. 2006; Zhou et al. 2017). Tables 1 and 2 summarizes the average coronary diameters for coronary segments in a healthy population measured with coronary angiography (Dodge et al. 2018). Several papers state a good correlation of coronary lumen diameter measurements of CT and coronary arteriography, especially for the proximal and midsegments (Sinha et al. 2006). Therefore, the coronary diameters mentioned can be used interchangeably between these imaging techniques. Because of the caliber of the IVUS probe, measurements can only be obtained in the proximal and midsegments of the coronary arteries, and diameter measurements may be influenced due to vasospasm related to vessel manipulation (Dickerson et al. 2010).